Control system



V. E. WHITMAN Jan. 9, 1934.

CONTROL SYSTEM Filed Aug. 50, 1950 4 Sheets-Sheet 1 1w umPm m 3 INVENTORVernon f. Whitman ATTORNEYS Jan. 9, 1934. v. E. WHITMAN 2,

CONTROL SYSTEM Filed Aug. 30, 1950 4 Sheets-Sheet 2 BY 7 W, Am,

ATTORNEYS Jan. 9,1934. v v. E, wHlTMAN 1,942,587

CONTROL SYSTEM Filed Aug. 30, 1930 4 Sheets-Sheet 5 INVENTQR Vernon EW/u Zman Jan. 9, 1934. v w N 1,942,587

CONTROL SYSTEM Filed Aug. 30, 1930 4 Sheets-Sheet 4 INVENT R 1 67/2022 5W/7/ mam Patented Jan. 9, 1934 CONTROL SYSTEM Vernon E. Whitman,Washington, D. 0., assignor to Hazeltine Corporation, Jersey City, N.J., a corporation of Delaware Application August 30, 1930. Serial No.478,041

7 Claims.

This invention relates to electrical control systems and particularly tosystems in which the control is efiected from a remote point, permittingoi electrically actuating an assemblage of parts or apparatus at adistance.

The invention is particularly adaptable to radio receivers ortransmitters where the control of tuning from a distant point isdesired.

In the present state of the art, where radio receivers have beenperfected in their tonal qualities to such high standards that they arecapable of reproducing musical renditions 01' a large orchestra in itsfull volume and brilliancy of tone, it is usually more pleasing to theaudience to listen to the program at a distance from the receiver, suchas the adjoining room or 'rooms. In such and other cases it is of greatconvenience to be able to change the resonant frequency of the receiverfrom that 01' one broadcasting station to that of another without goingto where the receiver is located, which in some cases may be aconsiderable distance.

The chief object of this invention is the provision of a remote controlsystem for actuating the tuning elements of a radio receiver ortransmitter whereby such receiver or transmitter can be accurately tunedto any desired frequency or station from a distant point.

An important feature resides in the use 01 the usual alternating currentsupply for actuating the control circuits, thereby greatly simplifyingthe electrical system as a whole.

Electrical systems for accomplishing this end have previously beenproposed, but such arrangements have been limited as to the number ofpossible settings, their operation required delicate tuning adjustments,and a great number of wires were necessary to connect the remote controlwith the radio tuning apparatus.

Furthermore such systems have required a direct-current source to supplythe remote control devices, while the radio apparatus itself operatedfrom the usual alternating current power lines, thus complicating andmaking more expensive the necessary equipment. All of thesedisadvantages are overcome by the present invention.

It is also desirable that the person using the remote control should beable to adjust the tuning of the apparatus to known positions oi. thetuning element and have means at the remote tuning point to indicate atall times the position of the tuning element.

In accordance with this invention, there is provided an electricallybalanced alternating current bridge network comprising a pair ofpotentiorneters, the variable contact of one of which is actuated at aremote point to unbalance the network and the variable contact of theother of which is actuated by the device to be controlled. Analternating current potential is supplied across one of the two pairs ofconjugate points 0! the network, or in other words, across each of thepotentiometers. The other 01 the two pairs of conjugate pointscomprising the variable contacts of the two potentiometers is connectedto an output circuit. When a current flows in the output circuit of saidnetwork, the output voltage is amplified and applied in the same phasethrough a common input circuit to each 01' the control grids of a pairof thermionic vacuum tubes. The separate plate or output circuits or thevacuum tubes are supplied 180 out of phase by the same alternatingcurrent potential, through the energizing coils oi! two selectivelyresponsive relays. A third relay is connected in the common leg of theoutput circuit 0! the tubes. The first two relays control the directionof rotation 01 areversible drive mechanism, such as a motor, whichmechanism is mechanlcally connected to the contact of the localpotentiometer as well as to the device to be controlled. The third relaycontrols the speed of rotation of the motor. The relays, whichconstitute control means independent of the drive mechanism, areresponsive to the magnitude of the current in the output of the networkand thus set the mechanism in operation. The tubes provide selectivemeans for discriminating between the phase 01' the current in the outputor the network relative to the current in the input circuit fordetermining the direction of operation 01' said mechanism, and controlthe current supplied to the reversible motor from a power source whichis separate and independent from the current passing through thenetwork.

While this invention in its preferred embodiment is herein illustratedand described as a remote tuning control for radio receivers, it will beobvious to anyone skilled in the art that it 106 can be advantageouslyapplied to control other devices where an accurate and flexible controlis to be effected from any distance.

The invention may be more clearly understood from a consideration oi.the accompanying draw- 10 ings in which:

Fig. 1 represents diagrammatically the electrical circuit of a controlsystem in accordance with this invention.

Fig. 2 shows the plate-voltage curves oi the no selector tubesv 21 and21' of Fig. 1 in reference to the signal voltage applied to their grids.

Fig. 3 represents the control system shown in Fig. 1 as applied to aradio receiver operating entirely from alternating-current power lines.

Fig. 4 shows a modification consisting in theis of Fig. 4.

Fig. 6 illustrates a modification of the invention in which analternating current relay replaces the selector tubes 21 and 21 and therelays 26 and 26' of Figs. 1, 3, 4 and 5.

Fig. 1, to which attention is now invited, shows an electricallybalanced alternating current network connected to control the action ofa reversible motor. The network includes two potentiometers 1 and 1'connected in'parallel as a bridge and supplied with alternating currentfrom the winding 3 of the transformer 2. Potentiometer 1, which shallhereinafter be referred to as the local potentiometer; has its movablecontact 6' mechanically connected to the device to be controlled. Thealternating current supply potential need not be high, and in practiceit has been found satisfactory to use about 50 volts, the resistancevalues of the potentiometers being 2,500 ohms each. The sliders 6 and 6,of the potentiometers are connected to the primary winding 8 of thetransformer 7. This transformer is of the audio-frequency type commonlyused in radio receivers and preferably of high, about 1:30, windingratio. The secondary winding 9 of the transformer 7, is tuned by meansof a condenser 10 to the frequency of the alternating current used inthe system, which under normal conditions is the house-lighting currentsupplied from the power-distributing station, usually of 25 or cycles.The winding 5 of the transformer 2 is the primary winding and connectsto the alternating current supply mains.

The amplitudeof the alternating voltage impressed on the primary winding8 of the transformer 7 depends upon the magnitude of the difference inposition of the potentiometer contact arms 6 and 6'; the phase of thisvoltage depends upon the sign of the algebraic difference in position ofthe potentiometer contacts 6 and 6'. Using the voltage supply to thepotentiometer from the winding 3 of the transformer 2 as the referencestandard, the phase of the voltage in the winding 8 of the transformer'7 shifts 180 as the algebraic difference in the position of the sliders8 and 6 changes sign. The output of the transformer 7 is connected tothe grid 12 of the tube 11 through the grid resistor 13, and to thecathode 17 in series with the battery 14 which supplies the necessarybiasing potential to the grid 12. The filament 17 of tube 11 is suppliedfrom the usual battery 15. The potential of the plate 16 of the tube 11is derived from the battery 53 through the coupling resistance 51. Thepurpose of this tube is to amplify the output of the transformer 7 andis shown as a resistance-coupled amplifier, the functioning of which iswell-known and need not be considered here.

The output circuit of the amplifier tube 11 is capacitively coupledthrough a condenser 52 to the common input circuit of a pair ofthermionic selector tubes 21 and 21. The filaments 24 and 24' of theselector tubes 21 and 21 are connected in parallel to the heatingbattery 28, the grids 22 and 22' of these tubes are connected togetherby wire 23. The required grid biasing potential is derived from thebattery 35 through the resistor 51.

The plate 25 of the tube 21 and the plate 25 of the tube 21' is suppliedwith an alternating potential through the energizing coils of the directcontrolling relays 26 and 26 from each end respectively of the winding 4of the transformer 2, the center tap of which forms the common returnfor the plate potential of both tubes through the energizing coil of therelay 2! to the filament 24 and 24 of the tubes 21 and 21.

It is clearly seen that the plate potential of the tube 21 and thereforethe voltage across the energizing coil of relay 26 will be 180 out ofphase with the plate potential of the tube 21, and the voltage acrossenergizing coil 26', and the plate current of both tubes will dependupon both the magnitude and the phase'of the voltage supplied to theirgrids, through the coupling to the output of the alternating currentnetwork.

A reversible series motor 29 with field windings 30 and 30 is shown asthe device to be controlled and is connected to the primary winding 5 ofthe transformer 2, through its field winding 30 in series with thecontacts 31 of the relay 26 or field winding 30 in series with contact31 of the relay 26'. Both contacts aforementioned are in series with thecontact 32, bridged by the resistance 33, of the relay 27, the circuitto the motor completed by wire 34 to the primary winding 5 of the,transformer 2. The reversible motor 21 is mechanically connected to themoving contact 6 of the local potentiometer 1'.

Thus the relays 26 and 26' are made selectively responsive to the phaseof the voltage impressed upon the input of the tubes 21 and 21', and themovement of the control potentiometer will cause the motor 29 to turn inone direction or the other to adjust the local potentiometer 1' torebalance the alternating current network. Whenever the difference ofthe settings of the potentiometers 1 and 1 exceeds a predeterminedamount, the third relay 27 will be actuated to short-circuit theresistance 33 and thus increase the speed of the motor 29. The operationof this system will be described more fully hereinafter.

Referring to Fig. 2 the curves 1 and 3 represent the instantaneous platevoltage of the tubes 21 and 21. The curves 2 indicate the grid voltagesof the same tubes referred to the same time scale as the curves 1 and 3.This will be explained in detail later.

Referring to Fig. 3 reference characters of Fig. 1, indicate identicalparts of the circuit, which shows the control system connected to aradio broadcast receiver of present day design having tunedradio-frequency stages in cascade. The operating potentials as well asthe filament heating currents for all tubes are derived from the commonpower transformer 2 which is identical to the one shown in Fig. 1,except that there are additional windings necessary for the operation ofthe radio receiver itself. The rectifier tube 36 supplies the necessarydirect-current pctentials to the plates and grids of all the tubes ofthe radio receiver including the amplifier .tube 11 of the controlsystem. These potentials are taken off from suitable taps of the voltagedividing resistor 37 which is grounded at the point 38, the positivepotentials being taken OH in 2. j

one direction and the negative potentials in another direction from thispoint.

The motor 29 is shown, diagrammatically, driving the rotor plates of thetuning condensers 39, 40, 41 and 42; and mechanically attached to theshaft 43 of the rotor plates is the arm 6' of the potentiometer 1'.condenser shaft 43 effects the tuning of the set and correspondinglymoves the contact arm 6' of the potentiometer 1 which also serves toindicate the position of the tuning condensers, above mentioned, on thescale 44' calibrated in suitable units such as meters or kilocycles.

The operation of the remote control tuning system is as follows: Themotor 29 is mechanically connected to the shaft of the tuning condensersor other tuning elements of the receiver. The two potentiometers 1 and1' are supplied with an alternating potential fromthe winding 3 of thepower transformer 2 and form an electrically balanced bridge circuit, aslong as their arms 6 and 6' rest at corresponding points of the twoscales 44 and 44', inasmuch as the resistance values on both sides ofboth arms 6 and 6' are equal and no current flows through the winding 8of the transformer 7 to which the arms 6 and 6' are electricallyconnected. In this condition of equilibrium the grid 12 of the vacuumtube 11 receives no impulse, and no change in grid voltage takes place.The amplifier tube 11, therefore, does not impress potential changes onthe grids of the selector tubes.21 and 21'. The

grids 22 and 22' of these tubes are so biased from the tap 47 of thevoltage dividing resistor 3'7 that practically no, or very little, platecurrent flows through the winding 4 of, the transformer 2 in series withthe energizing coils of the relays 26 and 26 and 27. The plate currentbeing zero or of such low value that it is not suflicient to actuate therelays referred to, the relay contacts will remain open and no currentcan flow to the field windings 30 or 30' of the motor 29.

Intuning the receiver from the remote point the contact arm 6 of theremote potentiometer 1 is moved in the desired direction correspondingto the markings of the scale 44 and brought to rest at a point on thisscale which indicates the wave length or the frequency 01' thebroadcasting station desired to be received. The change in position ofthe contact arm 6 to unbalance the network will result in thedisturbance of the electrical equivalence of the resistances of thebridge circuit, and an alternating current will flow through bothcontact arms 6 and 6 into the winding 8 of the transformer '7 from thewinding 3.of' the transformer 2 and thus impress across the output ofthe network an alternating current voltage. The amplitude of thiscurrent and the phase relationship of the input and output voltage willdepend upon the magnitude of the difference in position of the arm 6 ofthe potentiometer 1 relative to the arm 8' of the potentiometter 1'. Inother words the further the two contact arms are set in oppositedirections the greater will be the current flowing through them, and itwill reach its maximum value when one of the arms pointsto A while theother points to B, or vice versa.

The voltage impressed on the primary winding 8 of the transformer 7 isamplified by the tube 11 and impressed simultaneously on the grids 22and 22 of the selector tubes 21 and 21. The frequency of this voltagewhich is derived from the winding 3 of the power transformer 2 is, ofcourse, the same as the frequency of the The rotary motion of thevoltages in the other windings, determined by the frequency of the linevoltage supplied to the primary winding 5 of the same transformer, the

phase of the voltage impressed on the grid 22' and 22', however,relative to the plate voltage of the selector tubes will depend upon thesign of the algebraic difference in position of the two tion of the gridvoltage is clearly illustrated in the 3 curves of which 2m full line isthe instantaneous grid voltage for one condition of unbalance and thedotted curve is the instantaneous grid voltage for the other conditionof unbalance of the potentiometers as considered above. It will be seenthat in the first condition the grid voltage is in phase with the platevoltage of the tube 21' andthat in the second condition it is in phasewith the plate voltage of the tube 21.

To give a more clear definition of this important point, which is thesalient feature of this invention, let it be assumed that the arms ofthe potentiometers referred to are both at rest at a point C, midwaybetween the points A and B. It will be evident that the arm 6 of thepotensliders 6 and 6 of the potentiometers 1 and 1'.

tiometer 1 can be moved in either direction to- I a point between A andthe assumed point of rest C, the voltage then derived, and amplified bythe tube 11, will be impressed on the grids of the selector tubes 21 and21. The plate voltages of these tubes being 180 out of phase, theimpressed grid voltage will be in phase with the plate voltage of onlyone tube. Assuming that this tube is tube 21', the impressed voltage onits grid 22' will be out of phase with the plate voltage. This conditionwill tend to decrease any existing plate current, and the tube 21 willnot actuate any of the relays. On the other hand, the voltage impressedon grid 22 of tube 21 will be in phase with the plate voltage, andtherefore will be positive when the plate voltage is positive, causingan increase in the plate current. The increased plate current of tube 21flowing through the coils of relays 26 and 27 will be sufilcient toactuate the armature of relay 26 only and close the contacts 31, therebycompleting the circuit through the field 30 of the reversible motor 29.

The motor will then start to turn in a direction, so chosen by thecorrect connection of its field windings to the relay contacts 31 and31, that the turning of the tuning condenser shaft 43 will move thecontact arm 6' of the potentiometer 1 in such direction as to graduallydecrease the difference in the resistance values of the arms of thebridge circuit. When the contact arm 6' reaches the point correspondingto the setting of the arm 6, the bridge circuit resumes the state ofelectrical equilibrium, and the current in the primary winding 8 of thetransformer '7 ceases. This in turn reduces the plate current of thetube 21 to zero or to a awficlently low value to de energize the relay25 thereby breaking the circuit to the motor. It will be evident fromthe foregoing that this control system has great flexibility and gives asmooth continuous control over the tuning range, the action beingneither intermittent nor step by step.

The action of the third relay 2? with its associated resistor 33 furtherimproves the tuning operation by providing a speed control for the motor29. The speed of the motor is an important factor and must be slowenough to ensure that the momentum of the motor armature and associatedapparatus shall-not drive the contact arm of the potentiometer over thestopping point; for otherwise the motor would hunt back and forth beforestopping. A slow speed of the motor, on the other hand, lengthens thetime interval required for tuning from one setting to another,especially if the desired station is operating at a frequency remotefrom the one previously received. It is desirable, therefore, that thespeed of the motor be increased until the arm 6' of the potentiometer 1'is near the point where the desired station is indicated, and then inorder to insure fine tuning and avoid the overriding of the contact arm,the speed of the motor be decreased. The relay 27 accomplishes thisresult by controlling or regulating the speed of the motor in thefollowing manner. When the relay 27 is de-energized the contactpoints 32are open, and the current to the motor 29, provided that either one ofthe relays 26 or 28 is actuated, will flow through the resistance 33,the value of which is so chosen that the motor turns over at a speedthat will insure fine tuning and instantaneous stopping. The closing ofthe contacts 32 shunts the resistance 33 and the full line voltage willoperate the motor at greater speed. The relay 27 is so designed that itwill close at a predetermined value of current which is greater thanthat sufiicient to actuate either of relays 26 and 26'.

It has been above stated that the magnitudes of the currents in theplate circuits of the selector tubes 21 and 21 depend on the magnitudeof the difference in position of the arms 6 and 6'. The device operatesas follows: Let it be assumed that the receiver is tuned to a station ofrelatively low frequency, as indicated at the points A and A of thescales 44 and 44' and it is desired to tune in another station ofrelatively high frequency, as indicated at the points B and B. on thescales. The arm 6, therefore, is moved from the point A to the point B,and the maximum value of the voltage from the winding '3 of thetransformer 2 will be impressed on the winding 8 of the transformer 7and, as previously described, the plate current in one of the selectortubes 21 or 21' will reach a maximum value which energizes the relay 27and one of the relays, 26 or 26'. The resultant closing of contacts 32shunts the resistance 33 and the motor starts at full speed. Thetuning-condenser shaft, in turn, moves the contact arm 6' from the pointA towards B. The movement of the arm gradually decreases the impressedvoltage on the primary winding 8, thereby decreasing the plate current.As the arm 6' reaches a predetermined distance from the point B theplate current is decreased to such a small value that the relay 2'7opens, throwing the resistance 33 into the circuit and slowing down themotor. When the arm 6 reaches the point B the plate current in theselector tube becomes practically zero and whichever one of the relays26 or 26', was energized, opens and disconnects the motor from the line.

When tuning in stations closely allocated in frequency the magnitude ofthe voltage im pressed in the winding 8 due to the relatively littledifference in position of the arms 6 and 6'. will not cause a largeenough current-flow in the plate circuit of a selector tube to energizethe relay 27 and the motor will turn at slow speed due to the resistance33 in the circuit. It would, of course, be possible to employ anotherrelay like 27 to cut out an additional resistance, giving three speedsand so on; but inpractice it has been found that two speeds are adequateto cover the present broadcast bands. Instead of employing the relay 2'!and resistance 33 to provide an additional motor speed, other variablespeed devices may be used, as, for example, the coil and plunger 27 ofFig. 3 may operate a brake on the motor which will slow it up inproportion to the current flowing in the relay winding.

Figure 4 shows a simplified embodiment in the use of a polarized relay48 in place of the relays 26 and 26 of Figs. 1 and 3. Referencecharacters identical to those of the other figures indicate identicalparts of the circuits. The action of the polarized relay is similar tothe action of the relays 26 and 26', the contacts 31 and 31 leading tothe respective field windings 30 and 39' of the motor 29. The windings 4and 4' of transformer 2 are combined in the center-tapped encrgizingwinding of the relay 48. The plate current flowing in either half of therelay winding will attract the permanently magnetized armature 54 andclose either contacts 31' or 31 depending upon which half of the windingis energized.

Referring to Fig. 5, the circuit shows a modification of Fig. 4 in theuse of only one selector tube and a pair of balanced-armature relays.The operation of these relays in one direction depends on the rise ofthe current above a predetermined value, and in the other direction onthe decrease of the current below that predetermined value. Thecurrent-fiow in the energizing windings of both relays is the platecurrent of the tube 21, as both windings are in series between thefilament 24, the plate 25 and the potential source 4. The plate currentis so adjusted that when no signal voltage is impressed on the inputcircuit of tube 21 the plate current is of such value that it energizesthe relay coils sufficiently to attract the armatures so that they clearthe lower contacts but do not touch the upper contacts. During thisnormal plate current flow the armatures of the relays 27 and 49 arefloating midway between the contact points. Should the impressed voltageon the grid of the tube 21 be in phase with the plate voltage, aspreviously described, the rise in plate current attracts the armature ofthe relay 49 and the circuit will be completed through contact 31' toone of the field windings 39 of motor 29. However, should the impressedvoltage be out of phase with the plate voltage of tube 21 the normalplate current will drop to a considerably low value and the winding ofthe relay 49 becomes de-energized, allowing the armature to drop andcomplete the circuit to the motor through the lower contact 31 and tothe other field winding 30 of the motor. The action of the relay 27 issimilar to the previously described arrangements, except that it isadjusted to close at a predetermined maximum and also at a predeterminedminimum of plate current of the selector tube 21, therebyshort-circuiting the resistance 33 in both instances so as to increasethe motor speed. When the armature of relay 27 is floating the motorwill run at slow speed because resistance 33 will then decrease theseries-field current. In order that the armatures of relays 27 and 49may at such time remain out of contact, a suitable spring will berequired to balance the pull of the electromagnet. Fig. 5, nor in theother figures, because the constructions of relays of thetypes hereinreferred to are well known.

In reference to Figure 6, the arrangement shown is a modificationwithout the use of vacuum tubes. A specially constructed alternatingcurrent relay 59 selectively controls the closing of the motor circuit.Reference characters used in the previous figures designate partsidentical in the arrangements formerly shown. The relay 59 has a dividedcore 50 on either half of which connected in parallel are the fieldwindings 56 and 56. These windings are in such magnetic relation thatboth ends of the core 50 will be instantaneously similarly poled.

The armature 54 is pivoted on core portions 55 and equipped with fieldwindings 57 and 57'. The potentiometer 6 and 6' and the field windings56 and 56 of the relay 59 are supplied with alternating current from thesecondary winding 4 of transformer 2, the primary winding 5 of whichconnects to the house-lighting mains.

The armature windings 5'7 and 57 of the relay 59 are in series andaiding each other in magnetic polarity and connected to the contact arms6 and 6' of the potentiometers. In series with this circuit is the speedregulating relay 27, the purpose and action of which has been previouslydescribed and is shown with sliding contact over the resistance 33 inorder to give a more flexible control at a plurality of speeds. Thespeed controlling action of relay 27 is preferably so arranged throughwell-known electrical or mechanical devices as to maintain the motorspeed relatively high and fairly constant until the contact arm 6' ofpotentiometer 1 reaches a certain distance from the point of balance andthen decrease the speed of the motor 29 at a rate which will assureinstantaneous stopping at the desired point without unduly lengtheningthe time interval for the arm 6 in reaching it from its originalstarting point.

The action of the relay armature 54 in one way or the other depends uponthe phase relation between the current in the field winding and that inthe armature winding and there is thus provided selective relay meansfor discriminating between the phase of the current in the output of thenetworkrelative to the current in the input circuit. From the diagram itis clearly seen that the phase of the current in the armature windings57 and 57' shifts 180 as the algebraic diiierence in position of thepotentiometer contact arms changes sign, whereas the current in thefield windings 56 and 56' remains in uniform phase relation with thecurrent in the potentiometers. The movement of the relay armature ineither one direction closes the respective switch contacts whereby thecircuit is completed to one of the field windings 30 and 30 of the motor29.

I claim:

1. In a remote control system, as for actuating the tuning elements of aradio receiver; a reversible motor; a current source for said motor; tworelays for controlling the current to said Such springs are not shown inmotor to cause it to run in one direction or the other, respectively; athird relay for controlling the speed of said motor; an electricallybalanced alternating-current network including an alterhating-currentsupply, a local potentiometer mechanically connected to said motor, anda control potentiometer located at a remote point and operable tounbalance said network and thereby cause an alternating-current voltage,the phase of which will depend upon the relative settings of the twopotentiometers, to be impressed across the output of said network; and apair of thermionic tubes having a common input circuit coupled to theoutput of said network and having separate output circuits, each outputcircuit comprising the energizing coil of one of said directioncontrolling relays, an alternating-current voltage supply, the voltagein each circuit being 180 out of phase, and the energizing coil of saidthird relay, whereby the relays are selectively responsive to the phaseof the voltage impressed upon the input of said tubes, and movement ofthe control potentiometer will cause the motor to turn in one directionor the other, thus adjusting the local potentiometer to re-balance thealternating-current network, the third relay being operated to increasethe speed of the motor whenever the difference between the settings ofthe two potentiozneters exceeds a predetermined amount.

2. In a remote control system, as for actuating thetuning elements of aradio receiver; a reversible motor; a current source for said motor; apolarized relay having two energizing coils for controlling the currentto said motor to cause it to run in one direction or the other,respectivev 1y; relay means for controlling the speed of said motor; anelectrically balanced alternating-current network including analternating-current supply, a local potentiometer mechanically connectedto said motor, and a control potentiometer located at a remote point andoperable to unbalance said network and thereby cause analternating-current voltage to be impressed across the output of saidnetwork; and a pair of thermionic tubes having a common input circuitcoupled to the output of said network and having separate outputcircuits, each output circuit comprising one'of the energizing coils ofsaid polarized relay, an alternating-current voltage supply, the voltagein each circuit being 180 out of phase, and the energizing coil of saidspeed controlling relay means, whereby the polarized relay isselectively responsive to the phase of the voltage impressed upon theinput of said tubes, and movement of the control potentiometer willcause the motor to turn in one direction or the other, thus adjustingthe local potentiometer to re-balance the alternating-current network.

3. In a remote control system, as for actuating the tuning elements of aradio receiver; a reversible motor a current source for said motor; tworelays for controlling the current to said motor to cause it to run inone direction or the other, respectively; an electricaly balancedalternating-current network including an alternating-ourrent supply, alocal potentiometer mechanically connected to said motor, and a controlpotentiometer located at a remote point and operable to unbalance saidnetwork and thereby cause an alternating-current voltage to beimpressedacross the output of said network; and a pair of thermionictubes having a common input circuit coupled to the output of saidnetwork and having separate output circuits, each output circuitcomprising the energizing coil 01' one of said direction controllingrelays, and an alternating-current voltage supply, the voltage in eachcircuit being 180 out of phase, whereby the relays are selectivelyresponsive to the phase 01' the voltage impressed upon the input of saidtubes, and movement of the control potentiometer will cause the motor toturn in one direction or the other, thus adjusting the localpotentiometer to re-balance the alternating-current network.

4. In a remote control system, as for actuating the tuning elements of aradio receiver; a reversible motor; a current source for said motor; apolarized relay having two energizing coils {or controlling the currentto said motor to cause it to run in one direction or the other,respectively; an electrically balanced alternating-current networkincluding an alternating-current supply, a local potentiometermechanically connected to said motor, and a control potentiometerlocated at a remote point and operable to unbalance said network andthereby cause an-alternatingcurrent voltage to be impressed across theoutput of said network; and a pair of thermionic tubes having a commoninput circuit coupled to the output of said network and having separateoutput circuits, each output circuit comprising one of the energizingcoils of said polarized relay, and an alternating-current voltagesupply, the voltage in each circuit being 180 out of phase, whereby therelay is selectively responsive to the phase of the voltage impressedupon the input of said tubes, and movement of the control potentiometerwill cause the motor to turn in one direction or the other, thusadjusting the local potentiometer to re-balance the alternatingcurrentnetwork.

5. In a remote control system, as for actuating the elements of a radioreceiver; a reversible motor; two relays for controlling the current tosaid motor to cause it to run in one direction or the other,respectively; an electrically balanced alternating-current networkincluding two potentiometers one of which is mechanically connected tosaid motor and the other of which is located at a remote point andoperable to unbalance said network and thereby cause analternating-current voltage to be impressed across the output of saidnetwork; and a pair 01 thermionic tubes having a common input circuitcoupled to the output of said network and having separate outputcircuits, each output circuit comprising the energizing coil of one ofsaid direction controlling relays and an alternatingcurrent voltagesupply, the voltage in each circuit being 180 out of phase, whereby therelays are selectively responsive to the phase of the voltage impressedupon the input oi said tubes, thereby determining the direction ofrotation of the motor.

6. In a remote control system, a reversible drive mechanism, anelectrically balanced alternating current bridge network, a source ofalternating current of fixed voltage connected as an input circuitacross one pair of conjugate points of said network, an output circuitconnected across the other pair 01 conjugate points of said network,said last-mentioned points being adiustable to vary the output voltage,control means for adjusting one of said points and thereby disturbingthe balance of said networkto cause an alternating current to flow insaid output circuit, and control means independent or said drivemechanism responsive to the magnitude or said current for setting saidmechanism in operation and including selective relay means fordiscriminating between the phase of the current in .1

said output circuit relative to the current in said input circuit fordetermining the direction of operation of said mechanism.

'7. A remote control system in accordance with claim 6, in which thereversible drive includes a separate power source.

VERNON E. WHITMAN.

